Sergio Gonzalez headed home from a corner after four minutes for the visiting minnows and the Catalans missed a host of presentable chances as they failed to mount a comeback.

After a superb start to the season, Barcelona have lost three of their last six league games and won just one of those, with their lead whittled away.

Hansi Flick's side are level on points with Atletico Madrid, second, and lead third-place Real Madrid by a single point, having played one extra game than both their title rivals.

Barcelona started in the worst possible way as their former youth player Munir El Haddadi broke in down the right and forced a fine save from Inaki Pena at his near post.

From the resulting corner Leganes took the lead, with Sergio Gonzalez powering a header home to stun the Olympic stadium into silence.

From there Barcelona dominated against the visitors, 15th, and created several chances but found an inspired Marko Dmitrovic in their way.

The Serbian goalkeeper twice denied La Liga's top goalscorer Robert Lewandowski, who also headed over the bar from Jules Kounde's cross.

Dmitrovic produced a superb save to thwart Brazilian winger Raphinha, tipping his powerful effort against the crossbar.

Barcelona's teenage wing wizard Lamine Yamal hurt his ankle in a challenge in the first half but despite the pain affecting him, continued to play and was his team's most potent threat as usual.

The 17-year-old lashed narrowly over after gliding past Javi Hernandez as Barcelona turned the screw.

Despite his ankle issue and Ferran Torres warming up, Yamal emerged for the second half.

Kounde screwed a shot narrowly wide after Dani Olmo nudged the ball through for him.

Neither Lewandowski nor Olmo were on song and Flick replaced the pair with Torres and Fermin Lopez for the final 25 minutes.

Leganes held firm with Barcelona only able to create half-chances, until Raphinha and Torres combined to tee up Kounde, but he pulled his shot across the face of goal and wide.

In stoppage time, Barcelona won a free-kick on the edge of Leganes' area but Raphinha whipped it over the crossbar to end a thoroughly frustrating night.

Barcelona host Atletico in their final match of the year next weekend.